Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

112 Fluid Mechanics, Thermodynamics of Turbomachinery
Stage loading coefficient, y =D W/U 2
b 2
Specifying f, y, the unknown values of the loss coefficients, zR and zN, can be derived
using Soderberg’s correlation, eqn. (4.12), in which
From the above expressions the performance chart, Figure 4.13, has been derived.
An additional limitation is imposed on the performance chart because of the
reaction which must remain greater than or, in the limit, equal to zero. From eqn.
(4.22a),
Thus, at the limit, R = 0, the stage loading coefficient, y = 2.
w 2
a 2
c 2
FIG. 4.12. Velocity diagram for turbine stage with axial exit flow.
2.0
1.0
0
0.92
e R =140∞
0.90
0.875
120∞
0.85
0.80
U
100∞
w 3
0.75
0.70
0.2 0.4 0.6 0.8 1.0
Flow coefficient, f = cx /U
FIG. 4.13. Total-to-total efficiency contours for a stage with axial flow at exit.
c 3
80∞
b 3
60∞
40∞
20∞